Question

Define a chemical reaction in the context of biology.

What is a substrate?

Explain how enzymes lower activation energy.

What does it mean when an enzyme becomes “denatured”?

Give one example of a biological process that relies on enzymes.

Answer 1

1) Define a chemical reaction in the context of biology.
- A chemical reaction is a process in which chemical bonds are broken and/or formed so that reactant molecules are converted into different product molecules. In biology this includes the many transformations that occur in cells (e.g., breaking down food, building macromolecules, transferring chemical groups) and is governed by the same principles of kinetics and thermodynamics as nonbiological chemistry.

2) What is a substrate?
- A substrate is the specific reactant molecule upon which an enzyme acts. The substrate binds to the enzyme’s active site, where the enzyme catalyzes its conversion into one or more products.

3) Explain how enzymes lower activation energy.
- Activation energy (Ea) is the energy barrier that reactants must overcome to reach the transition state and be converted into products. Enzymes lower Ea by:
- Binding substrates in an active site to increase their effective concentration and properly orient them (proximity and orientation effects).
- Stabilizing the transition state through specific interactions, which lowers the energy of that state.
- Distorting substrate bonds (strain) to make them easier to break or rearrange.
- Providing an alternative reaction pathway (often involving transient enzyme-substrate intermediates).
- Offering a different microenvironment (e.g., acidic or basic residues, metal cofactors) that facilitates the chemistry.
Enzymes speed up the rate of reaction but do not change the overall free energy change (ΔG) or the position of equilibrium.

4) What does it mean when an enzyme becomes “denatured”?
- Denaturation means the enzyme’s native three-dimensional structure has been disrupted (unfolded or misfolded) by factors such as high temperature, extreme pH, or chemical agents. Because enzyme activity depends on its precise shape (especially the active site), denatured enzymes usually lose catalytic function. Denaturation can be reversible or irreversible depending on the severity and cause.

5) Give one example of a biological process that relies on enzymes.
- DNA replication: DNA polymerases are enzymes that catalyze the formation of phosphodiester bonds to synthesize a new DNA strand using a template. They also have proofreading exonuclease activity to correct errors, making replication both fast and accurate.